Hubble telescope reveals anti-ageing secret of white dwarfs: NASA

Hubble telescope has shown that some dying stars, particularly, the white dwarfs, have an anti-ageing secret that makes them appear much younger than they actually are, NASA revealed. Amazingly, the secret to the white dwarfs' anti-ageing regimen lies in a coating of Hydrogen that slows down their cooling so much that it ends up elongating their age by up to a whopping 1 billion years.

New evidence gathered by NASA’s Hubble Space Telescope suggests that white dwarf stars could continue to burn Hydrogen in the final stages of their lives, which in turn could cause them to appear more youthful than they actually are. NASA says that this discovery could have consequences for how astronomers measure the ages of star clusters, which contain the oldest known stars in the universe.

When a star dies, it could end up being a Black Hole, a Neutron Star or a White Dwarf Star based on its size and mass. Low-mass stars like our sun turn into white dwarf stars at the end of their life cycle. Before a star turns into a white dwarf star, it energises itself by fusing Hydrogen into the slightly heavier element called Helium. Once all of the Hydrogen is fused into Helium, it further fuses into heavier elements marking the end of a star’s life cycle and the beginning of the white dwarf star phase.

Now, an international group of astronomers has discovered the first evidence that white dwarfs can slow down their rate of ageing by burning Hydrogen on their surfaces.

“We have found the first observational evidence that white dwarfs can still undergo stable thermonuclear activity,” Jianxing Chen of the Alma Mater Studiorum Università di Bologna and the Italian National Institute for Astrophysics, who led this research said in a statement. “This was quite a surprise, as it is at odds with what is commonly believed,” he added.

To understand the white dwarf star evolution, astronomers compared cooling white dwarfs in two massive collections of star clusters M3 and M13. These two clusters share many physical properties such as age and metallicity but the populations of stars which will eventually give rise to white dwarfs are different.

Using Hubble telescope’s Wide Field Camera 3, the team of astronomers observed M3 and M13 at near-ultraviolet wavelengths, which allowed the researchers to compare more than 700 white dwarfs in the two clusters. They found that M3 contains standard white dwarfs, which are simply cooling stellar cores. While M13 contains two populations of white dwarfs: standard white dwarfs and those which have managed to hold on to an outer envelope of hydrogen, allowing them to burn for longer and hence cool more slowly. Comparing their results with computer simulations of stellar evolution in M13, the astronomers were able to show that roughly 70% of the white dwarfs in M13 are burning Hydrogen on their surfaces, which in turn was slowing down the rate at which they are cooling.

“Our discovery challenges the definition of white dwarfs as we consider a new perspective on the way in which stars get old,” Francesco Ferraro of the Alma Mater Studiorum Università di Bologna and the Italian National Institute for Astrophysics, who coordinated the study said in a release.

“We are now investigating other clusters similar to M13 to further constrain the conditions which drive stars to maintain the thin hydrogen envelope which allows them to age slowly,” he added.